This invention relates to human centrifuges. In particular, it relates to a self powered human centrifuge for use during periods of prolonged weightlessness in space.
During prolonged spaceflight, lack of gravity has many adverse effects on the human organism. These include cardiopulmonary deconditioning, shifts in body fluids and wasting of musculoskeletal structures.
On Earth, humans depend on gravity, a force defined as one "g", for many physiologic functions. In orbit or in prolonged spaceflight, conditions of near-zero "g" or "microgravity" exist. The physiologic effects of this environment have been extensively studied.
Humans will be subjected to prolonged periods of microgravity in the coming decades. A manned mars mission, slated for the first half of the twenty-first century will require over two years to complete the round-trip journey.
Existing experience has involved a limited number of subjects with microgravity durations of less than one year. From these data we know that returning subjects report dizziness and weakness sufficient to preclude walking. Most of these effects appear to be reversible with time on earth. The results of longer duration exposure is unknown.
The cardiopulmonary effects of flights greater than two weeks have demonstrated a 12% decrease in stroke volume (the amount of blood pumped per heart contraction) and an 11% decrease in left cardiac muscle thickness. The exercise capacity is decreased. Recovery time is related to the amount of inflight exercise rather than the mission duration.
Significant shifts in body fluid occur from the lower to the upper body in microgravity. In the upright position on earth, gravity holds fluids in the lower extremities. Muscles and venous valves help return fluid to the heart. Without gravity, fluids shift away from the legs. Leg volume decreases exponentially in the first 24 hours and plateaus within 3 to 5 days. With prolonged flights, a 15% decrease in calf circumference develops. Photographs of subjects' puffy faces attest to this effect. Subjects often complain of congestion.
Upon return to earth gravity, the fluid is rapidly shifted back to the lower extremities. This effect, known as orthostatic hypotension, can cause dizziness and loss of consciousness with disastrous results during re-entry and landing. Countermeasures such as ingestion of high-salt solutions and inflight use of a Lower Body Negative Pressure device can limit these effects. Positive pressure lower body suits are also utilized.
The effects of microgravity on the skeletal system are profound. Data from Soviet studies of the heel bone reveal bone loss in rough proportion to mission length with losses of up to 19.8% in flights up to 184 days. Some studies suggest that these losses may be irreversible upon return to earth. Urinary and fecal calcium losses persist throughout flight, raising the possibility of kidney stone formation. It has been calculated that one year in flight may result in sufficient undermining of bone strength so as to cause fracture. The presence of gravity as well as "impact loading" as occurs in normal walking are felt to be important in skeletal mass preservation.
Additional effects of microgravity have been noted in vestibular (balance), muscular, hormonal and other systems.
A currently used countermeasure is the exercise bicycle which is mounted to the space vehicle. A harness is utilized to keep the astronaut on the seat during exercise. Effective aerobic exercise is obtained. While pushing down on the pedals and being harnessed in, the astronaut can also generate a type of "weight bearing" of the lower extremities.
This stationary bicycle, however, does not produce a gravitational field. Body structures, such as the inner ear respond only to accelerations as in a gravitational field. Recent research indicates that some cells in the body are sensitive to gravitational fields. Therefore, it is desirable to produce such a gravitational field during prolonged spaceflight.
It is reasonable to assume that the temporary availability of a gravitational field during prolonged microgravity exposure will obviate some of these adverse consequences. A system for providing exercise as well as simulated gravity would be of considerable value for prolonged space flight.